1. Technical Field of the Disclosure
The embodiments disclosed herein relate generally to wireless communications, and more particularly, to a mechanism of a hybrid automatic repeat request (HARQ) operation in a semi-persistent scheduling (SPS) interval.
2. Description of the Related Art
In current system deployment, the 3rd generation partnership project (3GPP) has placed substantial focus on minimizing power consumption in a connected mode of a wireless communication system. For example, multiple solutions like a connected mode discontinuous reception (DRX) and SPS solution has been proposed (3GPP TS 36.321). The connected mode DRX reduces power consumption by finding an optimal trade off to wake up a user equipment (UE) only when data is scheduled. Further, the connected mode DRX, when used in conjunction with SPS, provides additional gain and avoids waking up the UE to read a control channel for downlink/uplink (DL/UL) resource allocation, because the SPS pre-defines UL/DL assignment with an SPS interval.
SPS is also proposed to support a high capacity Voice over Internet Protocol (VoIP) with reasonable control signaling. A principle of SPS includes persistent scheduling for initial transmissions and dynamic scheduling for retransmissions. In DL semi persistent scheduling, e.g., in Long Term Evolution (LTE), an eNodeB (eNB) may activate SPS using a Downlink control indicator (DCI) format in a physical downlink common control channel (PDCCH). After SPS is activated, the eNB may configure pre-defined DL/UL grant for a UE, which may remain valid for the SPS interval. For example, there could be N instances of resource allocation within the SPS interval. The eNB can de-activate the SPS using DCI format-0 in the PDCCH (with a specific configuration).
As per the current operation mode of SPS, after SPS has been activated in DCI format-0 using a special configuration (ref), an SPS grant may be available at an SPS assignment location for the SPS interval.
After the SPS interval, a new SPS grant may be sent by the eNB.
As indicated above, SPS has been designed for a Voice over Long Term Evolution (VOLTE) kind of operation, where a data requirement is generally known beforehand and remains constant, as per system design. In such cases, the SPS grant occurs at assigned instances for a given interval. However, current systems does not consider UE capability, where a UE can delay reading a DL SPS grant and can still have no impact on user experience. In most small cell deployment, a cell is heavily loaded and re-usability of available spectrum may add another dimension of power optimization, i.e., an eNB can send multiple grants to a UE, until UE does not send an acknowledgement/negative acknowledgement (ACK/NACK).
While the SPS and the connected mode DRX solutions provide substantial savings in power consumption, the SPS operation does not utilize the possibility of extending the UE sleep period, at the cost of extra resource allocation to the UE; especially, for small cell deployment, where full spectrum is available for a limited set of users and eventually underutilized.